Blue TiO2 nanotube arrays as semimetallic materials with enhanced photoelectrochemical activity towards water splitting

In the past years there has been a great interest in self-doped TiO₂ nanotubes (blue TiO₂ nanotubes) compared to undoped ones owing to their high carrier density and conductivity. In this study, blue TiO₂ nanotubes are investigated as photoanode materials for photoelectrochemical water splitting. Blue TiO₂ nanotubes were fabricated with enhanced photoresponse behavior through electrochemical cathodic polarization on undoped and annealed TiO₂ nanotubes. The annealing temperature of undoped TiO₂ nanotubes was tuned before cathodic polarization, revealing that annealing at 500 °C improved the photoresponse of the nanotubes significantly. Further optimization of the blue TiO₂ nanotubes was achieved by adjusting the cathodic polarization parameters. Blue TiO₂ nanotubes obtained at the potential of –1.4 V (vs. SCE) with a duration of 10 min exhibited twice more photocurrent response (0.39 mA cm^-2) compared to the undoped TiO₂ nanotube arrays (0.19 mA cm^-2). Oxygen vacancies formed through the cathodic polarization decreased charge recombination and enhanced charge transfer rate; therefore, a high photoelectrochemical activity under visible light irradiation could be achieved.     

Photocatalytic Crystalline and Amorphous TiO2 Nanotubes Prepared by Electrospinning and Atomic Layer Deposition

In this work core/shell composite polymer/TiO₂ nanofibers and from those TiO₂ nanotubes were prepared. First, poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) fibers were synthetized by electrospinning. They were covered with a 100 nm thick amorphous TiO₂ layer by atomic layer deposition at 50 °C. Later the polymer core was removed by two different methods: dissolution and annealing. In the case of dissolution in water, the as-prepared TiO₂ nanotubes remained amorphous, while when annealing was used to remove the polymers, the TiO₂ crystallized in anatase form. Due to this, the properties of amorphous and crystalline TiO₂ nanotubes with exactly the same structure and morphology could be compared. The samples were investigated by SEM-EDX, ATR-IR, UV-Vis, XRD and TG/DTA-MS. Finally, the photocatalytic properties of the TiO₂ nanotubes were studied by decomposing methyl-orange dye under UV light. According to the results, crystalline anatase TiO₂ nanotubes reached the photocatalytic performance of P25, while amorphous TiO₂ nanotubes had observable photocatalytic activity.     

含氯离子电解液中二氧化钛纳米管的阳极氧化形成机理及应用

采用电化学阳极氧化的方法,以氯化铵(NH₄Cl)水溶液为电解液,在纯钛表面制备了二氧化钛(TiO₂)纳米管。考察了制备电压、氧化时间、Cl^-浓度和钛基体的退火处理对阳极氧化过程的影响规律,探讨了在含氯离子电解液中纳米管的形成机理,并基于上述含氯离子电解液中纳米管形成机制,通过两步阳极氧化法得到无支撑纳米管薄膜。     

Synthesis of molecular imprinted polymer modified TiO2 nanotube array electrode and their photoelectrocatalytic activity

A tetracycline hydrochloride (TC) molecularly imprinted polymer (MIP) modified TiO₂ nanotube array electrode was prepared via surface molecular imprinting. Its surface was structured with surface voids and the nanotubes were open at top end with an average diameter of approximately 50 nm. The MIP-modified TiO₂ nanotube array with anatase phase was identified by XRD and a distinguishable red shift in the absorption spectrum was observed. The MIP-modified electrode also exhibited a high adsorption capacity for TC due to its high surface area providing imprinted sites. Photocurrent was generated on the MIP-modified photoanode using the simulated solar spectrum and increased with the increase of positive bias potential. Under simulated solar light irradiation, the MIP-modified TiO₂ nanotube array electrode exhibited enhanced photoelectrocatalytic (PEC) activity with the apparent first-order rate constant being 1.2-fold of that with TiO₂ nanotube array electrode. The effect of the thickness of the MIP layer on the PEC activity was also evaluated.     

Bi2WO6/TiO2纳米管异质结构复合材料的多模式下的光催化活性比较

以TiO₂纳米管为模板,采用多组分自组装结合水热法制备Bi₂WO₆/TiO₂纳米管异质结构复合材料。通过多种技术如X射线衍射（XRD）,X射线光电子能谱（XPS）,N₂吸附-脱附,扫描电镜（SEM）,高分辨透射电镜（HRTEM）和紫外可见漫反射吸收光谱（UV-Vis DRS）考察所制备样品的组成、结构、形貌、光吸收和电子性质。Bi₂WO₆纳米片或纳米粒子分布在TiO₂纳米管上,形成异质结构。随后,通过在紫外、可见和微波辅助光催化模式下降解染料罗丹明B（RhB）来评价复合催化剂的光催化活性。与TiO₂纳米管和Bi₂WO₆相比,Bi₂WO₆/TiO₂-35纳米管在多模式下表现出更优异的光催化活性。与紫外和可见降解模式相比,Bi₂WO₆/TiO₂-35纳米管在微波辅助光催化模式下对RhB的降解效率最高。这种增强的光催化活性源于适量Bi₂WO₆的引入、纳米管独特的形貌特征和降解模式所引起的增强的量子效率。降解过程中的活性物种被证明是h⁺,·OH和·O₂^-自由基。而且,在微波辅助光催化模式下,可产生更多的·OH和·O₂^-自由基。     

Synthesis,Characterization, and Photocatalytic Activity of N‐Doped TiO2 Nanotubes

N‐doped TiO₂ nanotubes with high photocatalytic activity were prepared by the combination of sol‐gel process with hydrothermal treatment. The prepared materials are characterized with transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), x‐ray diffraction (XRD), x‐ray photoelectron spectra (XPS), and UV‐vis spectra. Photocatalytic performance of the N‐doped TiO₂ nanotubes is studied by testing the degradation rate of methyl orange under UV irradiation. Obtained results indicate that N‐doped TiO₂ nanotubes have high catalytic activity for photocatalytic oxidation.     

The Preparation and Characterization of La Doped TiO2 Nanotubes and Their Photocatalytic Activity

La-doped TiO₂ nanotubes (La/TiO₂ NTs) were prepared by the combination of sol-gel process with hydrothermal treatment. The prepared samples were characterized by using transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectra, and ultraviolet-visible spectra. The photocatalytic performance of La/TiO₂ NTs was studied by testing the degradation rate of methyl orange under ultraviolet (UV) irradiation. The results indicated La/TiO₂ NTs calcined at 300°C consisted of anatase as the unique phase. The absorption spectra of the La/TiO₂ NTs showed a stronger absorption in the UV range and a slight red shift in the band gap transition than that of pure TiO₂ nanotubes. The photocatalytic performance of TiO₂ NTs could be improved by the doping of lanthanum ions, which is ascribed to several beneficial effects the formation of Ti-O-La bond and charge imbalance, existing of oxygen defects and Ti³⁺ species, stronger absorption in the UV range and a slight red shift in the band gap transition, as well as higher equilibrium dark adsorption of methyl orange. 0.75 wt% La/TiO₂ NTs had the best catalytic activity.     

Preparation and characterization of Zr doped TiO2 nanotube arrays on the titanium sheet and their enhanced photocatalytic activity

This paper described a new method for the preparation of Zr doped TiO₂ nanotube arrays by electrochemical method. TiO₂ nanotube arrays were prepared by anodization with titanium anode and platinum cathode. Afterwards, the formed TiO₂ nanotube arrays and Pt were used as cathode and anode, respectively, for preparation of Zr/TiO₂ nanotube arrays in the electrolyte of 0.1 M Zr(NO₃)₄ with different voltage and post-calcination process. The nanotube arrays were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV-Vis diffusion reflection spectra (DRS). The photocatalytic activities of these nanotubes were investigated with Rhodamine B as the model pollutant and the results demonstrated that the photocatalytic efficiency of Zr doped TiO₂ nanotubes was much better than that of TiO₂ nanotubes under UV irradiation. Zr/TiO₂ nanotube arrays doped at 7 V and calcined at 600 °C (denoted as TiO₂-7 V-600) achieved the best photocatalytic efficiency and the most optimal doping ratio was 0.047 (Zr/Ti). TiO₂-7 V-600 could be reused for more than 20 times and maintained good photocatalytic activities.     

Electrogenerated chemiluminescence of anatase TiO₂ nanotubes film

Highly ordered titanium dioxide (TiO₂) nanotubes film was successfully synthesized via anodic oxidation of a Ti foil in an ammonium fluoride-based ethylene glycol solution. The electrogenerated chemiluminescence (ECL) behavior of the resulting TiO₂ nanotubes film was subsequently studied. Strong ECL emission was observed at −1.40 V (vs. Ag/AgCl) and the ECL spectrum displayed three emission peaks which were bathochromatically shifted by ca. 140 nm as compared to its corresponding photoluminescence (PL) emission peaks, indicating that the surface state plays an important role in the emission process. The ECL emission can also occur in a deareated solution attributing to the surface adsorbed O₂ molecules. The ECL emission intensity was quenched by dopamine and greatly enhanced in the presence of dissolved O₂ and H₂O₂, making it possible to detect these analytes. The TiO₂ nanotubes film has been successfully applied to determine the dissolved O₂ content in river and pond water samples, the H₂O₂ concentration in commercial disinfectant samples and the dopamine concentration in commercial dopamine injections with satisfactory results. The plausible ECL mechanisms of TiO₂ nanotubes film in aqueous solution are discussed.     

Tribological behavior of polyurethane-based composite coating reinforced with TiO2 nanotubes

The unmodified and hexamethylene diisocyanate (HDI) modified TiO₂ nanotubes, were used for fabricating TiO₂ nanotubes (TiNTs)/polyurethane (PU) composite coating. The effects of applied load and sliding speed on the tribological behavior of the composite coating were investigated using a block-on-ring wear tester. Compared to the TiO₂ nanotubes filled PU composite coating, the HDI modified TiO₂ nanotubes (TiNTs-HDI) filled one had the lower friction coefficient and higher wear life under various applied loads and sliding speed. Scanning electron microscope (SEM) investigation showed that the TiNTs-HDI filled PU coating had smooth worn surface under given applied load and sliding speed, and a continuous and uniform transfer film formed on the surface of the counterpart ring, which helped to reduce the wear of the coating. The improvement in the tribological properties of TiNTs-HDI/PU composite coating might due to an improvement in interfacial adhesion between TiNTs and PU after HDI treatment. The strong interfacial coupling of the composite coating made TiNTs-HDI not easy to detach from the PU matrix, and prevented the rubbing-off of PU composite coating, accordingly improved the friction and wear properties of the composite coating.     

TiO2–carbon nanotube heterojunction arrays with a controllable thickness of TiO2 layer and their first application in photocatalysis

TiO₂–carbon nanotube (CNT) heterojunction arrays on Ti substrate were fabricated by a two-step thermal chemical vapor deposition (CVD) method. CNT arrays were first grown on Ti substrate vertically, and then a TiO₂ layer, whose thickness could be controlled by varying the deposition time, was deposited on CNTs. Measured by electrochemical impedance spectroscopy (EIS), the thickness of the TiO₂ layer could affect the photoresponse ability significantly. About 100 nm thickness of the TiO₂ layer proved to be best for efficient charge separation among the tested samples. The optimized TiO₂–CNT heterojunction arrays displayed apparently higher photoresponse capability than that of TiO₂ nanotube arrays which was confirmed by surface photovoltage (SPV) technique based on Kelvin probe and EIS. In the photocatalytic experiments, the kinetic constants of phenol degradation with TiO₂–CNT heterojunctions and TiO₂ nanotubes were 0.75 h⁻¹ (R² = 0.983) and 0.39 h⁻¹ (R² = 0.995), respectively. At the same time, 53.7% of total organic carbon (TOC) was removed with TiO₂–CNT heterojunctions, while the removal of TOC was only 16.7% with TiO₂ nanotubes. These results demonstrate the super capability of the TiO₂–CNT heterojunction arrays in photocatalysis with comparison to TiO₂-only nanomaterial.     

Optimizing TiO2 nanotube morphology for enhanced photocatalytic H2 evolution using single-walled and highly ordered TiO2 nanotubes decorated with dewetted Au nanoparticles

In the present work we introduce the formation of highly ordered single-walled TiO₂ nanotubes based on anodizing nanoimprinted titanium substrates. In a first step, anodization on nanoimprinted substrates leads to the formation of highly ordered TiO₂ nanotubes. These as-formed TiO₂ nanotubes have a double-walled nature. After an optimized chemical treatment in piranha solution, the inner wall is removed and an array of single-walled TiO₂ nanotubes is obtained that has a high degree of hexagonal ordering. These single walled arrangements show an enhanced photocatalytic activity for H₂ evolution in comparison with classic self-ordered TiO₂ nanotubes.     

In Situ ATR-FTIR and UV-Visible Spectroscopy Study of Photocatalytic Oxidation of Ethanol over TiO2 Nanotubes

The photocatalytic oxidation of ethanol over TiO₂ nanotubes (NTs) was investigated by in situ attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR) and ultraviolet (UV)-visible spectroscopy. In the ATR-FTIR study, the TiO₂ NTs were spread in a ZnSe crystal trough that was used as the reactor. The evolution of the reaction under UV irradiation was investigated by in situ monitoring of changes in the species at the surface of the TiO₂ NTs. Ethanol adsorbed on the TiO₂ NTs surface, forming alkoxide and hydroxide groups, which were then attacked by ^?OH, with the formation of a vinyl alcohol intermediate that was finally transformed to acetic acid. In addition, the species changes in the reaction solution were also investigated by in situ UV-visible spectroscopy using a small volume flow-through cell. The UV-visible data further confirmed the oxidation mechanism of ethanol on TiO₂ NTs elucidated by ATR-FTIR data.     

Label-free Photoelectrochemical Aptasensor for the Determination of Carcinoembryonic Antigen Using a Cadmum Sulfide Quantum Dot Sensitized Titanium (IV) Oxide Nanotube Electrode

A label-free photoelectrochemical aptasensor for the sensitive and selective determination of carcinoembryonic antigen was constructed based on a CdS quantum dot sensitized TiO₂ nanotube electrode. TiO₂ nanotubes with highly ordered structure and more active sites than bulk TiO₂ were prepared with an electrochemical anodic oxidation process. The CdS quantum dots were immobilized on the TiO₂ nanotubes using poly(diallyldimethylammonium chloride) as a bridge. Due to the energy level match between TiO₂ and CdS, the CdS quantum dots/TiO₂ nanotubes electrode exhibits excellent photoelectrochemical performance. The large surface area of the electrode also allows for capturing large numbers of aptamers. The fine photoelectrochemical performance and the large surface area of the electrode greatly enhanced the detection sensitivity. Under the optimal conditions, the prepared photoelectrochemical aptasensor presents desirable analytical properties for the determination of carcinoembryonic antigen in the range of 0.05 to 10?ng?mL^?1 with a detection limit of 0.014?ng?mL^?1. The application of the designed protocol was investigated by analyzing carcinoembryonic antigen in human serum samples with recoveries from 80.0 to 115.0%. This simple and sensitive method provides an alternative tool to standard biochemical assays.     

Influences of the H2PtCl6 Solution's pH on the Photocatalytic Activities of Platinum-Loaded TiO2 Nanotubes

By using H₂PtCl₆ and titanate nanotubes as precursor, platinum-loaded TiO₂ nanotubes (Pt/TiO₂NTs) are prepared at different pH by deposition-precipitation method. The prepared materials are characterized with powder x-ray diffraction (XRD) and x-ray photoelectron spectra (XPS). Their photocatalytic performance is evaluated by the degradation rates of methyl orange solution under UV-vis light irradiation. Obtained results indicate that the pH of H₂PtCl₆ solution has obvious influence on the catalytic performance of Pt/TiO₂NTs.     

CdS/TiO2纳米管复合结构的制备与光电性能研究

利用阳极氧化法在钛金属基体表面制备一层TiO₂纳米管阵列薄膜, 然后通过水热反应在TiO₂纳米管上负载CdS纳米粒子, 形成CdS/TiO₂纳米管的复合结构。利用SEM、XRD、XPS、UV-Vis等手段对其形貌和结构进行表征。进一步考察了CdS/TiO₂纳米管的光电性能和光催化活性, 结果表明, 相比于TiO₂纳米管, CdS/TiO₂纳米管复合结构在紫外光和可见光下都具有更好的光催化活性及光电性能。     

TiO2纳米管修饰镍电极及其光催化辅助电解水制氢性能研究

本文通过水热法制备二氧化钛纳米管(TiO2NT),并用制备的TiO2NT对碱性电解水制氢装置的镍片阳极进行修饰,在电解水的基础上,通过光催化与电解过程的耦合,提出并实现了光催化辅助电解水制氢过程。通过XRD、UV-Vis、FE-SEM、AFM和光催化辅助电解水制氢等方法对试样的结构和性能进行了表征和测试。结果表明,在紫外光照条件下,用TiO2NT修饰镍片阳极的光催化辅助电解水过程的产氢速率比单纯电解水提高了61%。     

CdS/TiO2纳米管复合结构的制备与光电性能研究

利用阳极氧化法在钛金属基底表面制备一层TiO2纳米管阵列薄膜,然后通过水热反应在TiO2纳米管上负载CdS纳米粒子,形成CdS/TiO2纳米管的复合结构。利用SEM、XRD、XPS、UV-Vis等手段对其形貌和结构进行表征。进一步考察了CdS/TiO2纳米管的光电性能和光催化活性,结果表明,相比于TiO2纳米管,CdS/TiO2纳米管复合结构在紫外光和可见光下都具有更好的光催化活性及光电性能。     

Hierarchical TiO2 nanosheet‐assembled nanotubes with dual electron sink functional sites for efficient photocatalytic degradation of rhodamine B

A novel Pt–TiO₂/Ag nanotube photocatalyst has been synthesized successfully via a facile method. TiO₂ nanotubes are assembled with numerous ultrathin TiO₂ nanosheets and show a highly open structure. The gaps between adjacent TiO₂ nanosheets can serve as channels for the access of reactants, accelerating the mass transfer process. During the fabrication process of the Pt–TiO₂/Ag nanotube photocatalyst, high‐quality Pt–SiO₂ nanotubes are synthesized first with the structure‐directing effect of polyvinylpyrrolidone. Then a TiO₂ layer is coated on the outside surface of the silica nanotubes. The introduced titanium species can be converted into TiO₂ nanosheet structure during the subsequent hydrothermal treatment, gradually constructing nanosheet‐assembled nanotubes. Lastly, after the introduction of another electron sink function site of Ag through UV irradiation, the Pt–TiO₂/Ag nanotube photocatalyst with dual electron sink functional sites is obtained. The specially doped Pt and Ag NPs can simultaneously inhibit the recombination process of photogenerated charge carriers and increase light utilization efficiency. Therefore, the as‐synthesized Pt–TiO₂/Ag nanotube catalyst exhibits a high photocatalytic degradation performance for rhodamine B of 0.2 min^?1, which is about 3.2 and 5.3 times as high as that of Pt–TiO₂ and TiO₂ nanotubes because of the enhanced charge carrier separation efficiency. Furthermore, in the unique nanoarchitecture, the nanotubes are assembled with numerous ultrathin TiO₂ nanosheets, which can absorb abundant active species and dye molecules for photocatalytic reaction. On the basis of experimental results, a possible rhodamine B degradation mechanism is proposed to explain the excellent photocatalytic efficiency of the Pt–TiO₂/Ag nanotube photocatalyst.     

TiO2 Nanotubes as a Therapeutic Agent for Cancer Thermotherapy

We report the photothermal properties as well as the in vitro cell test results of titanium oxide nanotubes (TiO₂ NTs) as a potential therapeutic agent for cancer thermotherapy in combination with near-infrared (NIR) light. TiO₂ NTs are found to have a higher photothermal effect upon exposure to NIR laser than Au nanoparticles and single-wall carbon nanotubes, which have also attracted considerable interest as therapeutic agents for cancer thermotherapy. The temperature increase of a TiO₂ NT/NaCl suspension during NIR laser exposure is larger than that of a TiO₂ NT/D.I. water suspension due to the heat generated by the formation of Na₂TiF_6. According to the in vitro cell test results the cells exposed to NIR laser without TiO₂ NT treatment have a cell viability of 96.4%. Likewise, the cells treated with TiO₂ NTs but not with NIR irradiation also have a cell viability of 98.2%. Combination of these two techniques, however, shows a cell viability of 1.35%. Also, the cell deaths are mostly due to necrosis but partly due to late apoptosis. These results suggest that TiO₂ NTs can be used effectively as therapeutic agents for cancer thermotherapy due to their excellent photothermal properties and high biocompatibility.